We were just informed by our SIM card provider that they are performing an unscheduled maintenance to correct a system performance issue.
During the period of maintenance if your tracker is actively updating online (existing session) it will not be affected.
If the tracker is not already updating but trying to connect (new session), it won't be able to connect but will cache the GPS data and send later once the network is available.

We sincerely apologize and will update this post as more information is available.

[UPDATE 5/3/2016 10:30PM EDT]: The SIM card provider has completed the maintenance with performance issue fixed. All systems back to normal.